Question Decreasing the Breathing Reflex....Possible?

[Duke Dive Medicine]

It seems like the WoB would be terrible... I guess "breathing" would be handled by some kind of forced circulation via intubation?

Therein lie two of the reasons why liquid breathing in humans is impractical with present technology.

Best regards,
DDM

 

[Sure Squintsalot]

This thread mixes two different topics: liquid breathing and breathing stimulus.

Correct.

In rooting around a few moldy boxes in the internet basement, I came across this interesting paper:

Shouldn't have been surprised that the Office of Naval Research funded the work; having a way to escape a submarine was a hot topic, and maybe still is. At any rate, gas exchange in fluids, as noted in the abstract is a limiting factor; if gas exchange is too slow to allow a human to do work, it's pretty useless, at least in the above 1970s era context. Other papers I've found mention CO2-laden fluids needing to pumped (somehow) from lungs and replaced with fresh fluid. "Liquid Breathing" is also a current hot topic in the field of emergency neonatal care, which I did not know.

Here's the complete abstract of the above paper:

"The maximum effective alveolar ventilation (VAemax) in healthy young liquid breathing men is approximately 3 1/min. This estimate is based onmeasured expiratory flows of saline and FC-80 fluorocarbon liquid from excised dogs' lungs and maximum expiratory flow and gas exchange in saline ventilated lungs of men. At a solubility of CO, in saline of 0.742 ml STPD/l/mmHg, aVAemax of 3 1/min precludes the feasibility of saline breathing in man. Normothermic anesthetized dogs ventilated with oxygenated FC-80 fluorocarbonliquid can be maintained at a normal PaCd- for 1 hr.- This indicates that the solubility of C02 in FC-80 fluorocarbon liquid as approximately 3 ml STFD/l/wukg, which is considerably higher than2reported in the literatureIt should be possible for a healthy man brearhin jixygenated FC-60 fluorocarbon to maintain a normal PaCO2 while at rest. (this would make possible the rapid escape from disabled submarine at great depth. The use of an emulsion of 1% (by volume) of 2 M NaOH in FC-80 fluorocarbon liquid should permit a liquid breathing diver to perform work requiring a VO2 of approximately 11 STPD/min while maintaining a normal PaC02. Microexamination of the lungs of dogs and rats that had breathed oxygenated FC-80fluorocarbon liquid or an emulsion of 1% (by volume) of 2 M NaOH in FC-80fluorocarbon liquid revealed the transient presence of increased numbers of mononuclear cells but no other pathologic changes.

Here's the link for anyone interested: http://archive.rubicon-foundation.org/dspace/bitstream/123456789/4257/1/ADA037089.pdf

It's never clear whether or not the breathing reflex is eliminated but must be forced by some mechanical means.

 

[TrimixToo]

You can suppress the breathing reflex with high-dose opiates and some kinds of anesthesia.

Probably not the best choices while diving, but I couldn't resist.

 

[dmaziuk]

It seems like the WoB would be terrible... I guess "breathing" would be handled by some kind of forced circulation via intubation?

IIRC the idea was that at high enough pressures it'll be less that WOB on compressed gas -- given the right liquid.

As I recall O2 delivery was fine but they could never get the CO2 removal part working.

 

[John C. Ratliff]

This thread mixes two different topics: liquid breathing and breathing stimulus.
I am not aware of any connection between these two topics.
My knowledge of liquid breathing is very limited, indeed, not exceeding what one can learn on the wikipedia: Liquid breathing - Wikipedia.
Instead I have some knowledge on methods for diminishing or entirely suppressing the breathing stimulus, as I was trained to free diving, back in the seventies.
At that time it was generally considered useful to teach free divers about these methods, which allow to extend the time spent breath holding.
But they also expose to serious risks of anoxy, which I experienced twice, passing out while training in a pool.
The breathing reflex can be suppressed acting on two factors:
1) reducing the amount of CO2 in the body by long and deep hyperventilation.
2) Increasing the threshold of CO2 concentration which triggers the reflex, by training the body to withstand progressively higher CO2 concentration (breath holding just after intense muscular efforts).
Albeit the two things require completely different, opposite training procedures, the end result is that a free diver is made capable of burning all the oxygen in his lungs before feeling the need to breath.
And this yields to passing out, which can be very dangerous if there is no proper surveilliance and fast rescue.

This is now known as "Shallow Water Blackout," and the potential for passing out has two somewhat different mechanisms. One is described above, whereby there is a decrease in CO2 due to hyperventilation, and also some tolerance to CO2. This can happen in a pool. The second mechanism has to do with breathhold diving to depth, using the hyperventilation techniques, and then ascending where the decreasing pressure causes a reverse in the osmosis diffusion* in the lungs, and O2 actually can travel from the blood into the lungs, causing blackout as the diver approaches the surface.

I have a PDF of this concept that I revised on 11-7-2022, and it includes the following graphs to explain better this process. If you want to see the entire explanation, please PM me with your e-mail.

SeaRat

*Thanks JohnDiver99 for the correction. "osmosis is the diffusion of water molecules, not other constituents... FYI"

 

[Dr Simon Mitchell]

Can anyone explain why diving with enriched air (or even with pure oxygen) doesn't lessen the breathing reflex?

Hello,
In fact, it does. Several other commentators on this thread have correctly pointed out that the most important influence on the drive to breathe is generated by carbon dioxide levels in the arterial blood - higher CO2 = greater drive to breathe. However, if you have a higher arterial oxygen level, then the drive to breathe generated by increasing CO2 levels is reduced. You can easily try this yourself if you have a cylinder of oxygen connected to a scuba regulator (oxygen clean of course!!). Time yourself holding your breath on air, and then try the same after washing oxygen into your lungs (eg 10 breaths on the scuba regulator). You will notice a significant difference in the time and the subjective perception of breath hold discomfort. To summarize this, although increasing CO2 level is the primary driver of breathing, this is definitely modified by oxygen levels (less drive to breathe is oxygen is high, more drive to breathe if oxygen is low).

Don't record-chasing freedivers experience some elimination of that reflex as they hold the torpedo weight and plummet to high pressure depths where oxygen is literally cold-pressed through aelveolar membranes?

Yes, this is essentially true although 'cold-pressed' is not really the right term. The lungs get compressed rapidly so even though the diver is apnoeic and consuming oxygen, the pressure of oxygen in the lungs increases during the rapid descent. We demonstrated the latter phenomenon in a 2021 study where we measured the arterial oxygen levels in an elite freediver at ~200' / 60m. The related paper has been published and can be read on PMC for free here.

Simon M

 

[dmaziuk]

Time yourself holding your breath on air, and then try the same after washing oxygen into your lungs (eg 10 breaths on the scuba regulator). You will notice a significant difference in the time and the subjective perception of breath hold discomfort. To summarize this, although increasing CO2 level is the primary driver of breathing, this is definitely modified by oxygen levels (less drive to breathe is oxygen is high, more drive to breathe if oxygen is low).

Is that the oxygen levels or washing out residual CO2 from your lungs though? You could achieve the same effect if you hyperventilate for 10 breaths.

 

[Dominik_E]

It is not only the "purging" of CO2 from the lungs; pre-breathing O2 results in generally longer apnea times than doing the same pre-breathing pattern with air. The higher O2 concentration in effect also lessens the chemoreceptor response to the rise of the CO2.

But I would like to comment on the question of air consumption with nitrox vs. air; surely the effect mentioned above is there, and so surely -- all else being equal -- there will be somewhat less urge to breathe on nitrox, compared to air. However, I would not be surprised if that does not translate in less real-life consumption: If you observe fellow divers, normally they are breathing already more often than would be the case under the same exercise on dry land. Breathing patterns in scuba diving seem largely governed by habits, and surely also by some subconscious effects from immersion (e.g. the famous "inversion" from inhale - exhale - pause - inhale... to inhale - pause - exhale - inhale...) that happens for many folks. So I would not bet on longer dive times with nitrox due to less consumption.

 

[dmaziuk]

It is not only the "purging" of CO2 from the lungs; pre-breathing O2 results in generally longer apnea times than doing the same pre-breathing pattern with air.

That's not necessarily a contradiction: if you're pre-breathing oxygen, you are not inhaling the 0.04% CO2 that you get with every breath of air, so some amount of "purging" is taking place. (And if our deco models work, the drop in alveolar PPCO2 results in accelerated washout of CO2 from the blood as well.)

What I was wondering is if that might be enough to mess with the urge to breathe. It sounds like very little, but how little is "too little"?

 

[BoundForElsewhere]

Therein lie two of the reasons why liquid breathing in humans is impractical with present technology.

Best regards,
DDM

Damnit.